4Q15 5week Test Notes
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Concept 1: Gravity
How do I increase the force of gravity on an object?
Change:_____Mass of m1 ______
Change: ___Mass of m2______
Change:____The distance r between them______
Concept 2: Weight and Mass
What is mass?__The amount of matter in an object (count of electrons, protons, neutrons)
What is weight?___The pull of gravity on a mass______
Concept 3: Inverse square law
What is the inverse square law?_The rule affecting certain phenomena in which the strength of the phenomena decreases as the square of the distance increases.______
Name some examples of things it applies to:_____Gravity, light, sound, the effect of electric charge______
______
Problems:
1) What is the mass of a 10kg object on Jupiter (where gravity is 3x stronger than the Earth’s?)______10kg______
2) What is the weight of a 10 pound object on the moon (where the force of gravity is 1/6 that of the Earth?)______10/6 pounds______
______
3) If I double the mass of an object, how does that affect the force of gravity acting on the object?______2x______
4) If I double the mass of the Earth, how does that affect the weight of my 10 pound cat?
______2x______
5) If I double the distance between my cat and the Earth, how does that affect his weight?
______Reduces by 2-squared (4 times)______
What is my cat’s new weight?___(10/4) pounds______
6) If I triple the distance between my cat and the Earth, how does that affect his weight?
______reduces by 3-squared (9 times)______
What is my cat’s new weight?____(10/9) pounds______
7) What is my cat’s name?______Mwane______
8) What is the mass of my 10 pound cat? (Hint: The mass of a 1 pound object is 1/(2.2kg) on the Earth’s surface.______(10/2.2) = 4.5 kg______
9) Why do I need to tell you where my cat is before you can answer the question above?
Mass does not change, weight is totally dependent on where in the universe you are.
Concept 4: Fields around magnets
Magnetic fields are strongest at the ends of a magnet. Like poles repel, unlike poles attract.
There is no such thing as a single N or S pole – every magnet has both.
1. What can be changed to increase or decrease the current induced in a coil through which a magnet is being moved?
- Change velocity (increase)
- Change the strength of the field (increase)
- Change the number of coils (increase)
Go to: http://phet.colorado.edu/en/simulation/faraday to review this further.
Concept 5: When a generator is connected to a circuit, it is harder to turn than when it is not connected. This is largely because when it is connected, you need energy to push the electrons, which increases the difficulty in moving the generator. What you are feeling is the generator “pushing back” to try to keep you from moving the electrons. So…push harder!
Concept 6: A current through a wire produces a magnetic field. A wire moving through a magnetic field produces a voltage.
Field around a wire: http://www.fed.cuhk.edu.hk/sci_lab/Simulations/phe/mfwire.htm
Concept 7: Magnetism starts at the level of the atoms. Magnetic material forms in domains. In a permanent magnet, these domains stay fixed. In a “soft” magnet, the domains are ordered only while there is magnetic field.
In a non-magnetic material, there are no domains.
Concept 8: Newton’s Law of cooling: The temperature of an object cools fastest the farther it is away from the ambient (room) temperature. Or, the temperature of an object heats up fastest the farther it is away from the ambient (room) temperature.
Below is a graph of an object cooling in a room.
Approximately how fast is the object cooling when it starts?____2 degrees per minute_____
______
Approximately how fast is the object cooling at the end of the period?_1/2 degree per minute
______
If the room temperature is 25C, what is your best guess as to how long it will take the object to get to room temperature?
a) About 20 minutes
b) About 40 minutes
c) It will never get there.
Concept 9: Convection moves heat away from a heat source by causing a fluid to expend, become less dense, and rise.
Concept 10: Radiation uses light (usually non-visible infrared light) to carry heat in the form of energy. Thermal radiation acts just like light – moves in a straight line and is best absorbed by black objects. Thermal radiation diminishes as the distance increases from the source due to the inverse-square law.
1) If I double the distance between me and a heat source (say, the Sun), how does the amount of energy I receive change?____Reduces it by 2-squared (4)______
2) If I triple the distance between me and a heat source (say, the Sun), how does the amount of energy I receive change?_____ Reduces it by 3-squared (9)______
3) If I quadruple the distance between me and a heat source (say, the Sun), how does the amount of energy I receive change?_ Reduces it by 4-squared (16)______
Concept 11: Bernoulii: Bernoulli’s principle states that the faster a fluid is moving, the lower its pressure.
For an airplane wing, that means if the air is moving faster on top of the wing, the pressure is lower at the top than at the bottom, and the wing has “lift”.
For a house, that means a fast moving stream of air going across the roof may serve to lift the roof off the house.
For a spoiler, that means that the fast moving stream of air below the spoiler will provide negative “lift” and serve to push the tires more firmly to the road.
Concept 12: Temperature scales
There are three major temperature scales in use: Fahrenheit, Celsius, and Kelvin. Fahrenheith is the common temperature scale in the USA, while Celsius is common in the rest of the world. Kelvin is similar to Celsius but starts at a different point (absolute zero) instead of the freezing point of water.
F = (9/5) C + 32
C = (5/9) (F - 32)
K = C + 273, or C = K -273
The following table shows some points of interest regarding these three scales:
Fahrernheit / Celsius / KelvinBoiling point of water / 212°F / 100°C / 373K
Body temperature / 98.6°F / 37°C / 310K
Room temperature / 70°F / 21°C / 294K
Freezing point of water / 32°F / 0°C / 273K
Absolute zero / -460°F / -273°C / 0K